Human immunodeficiency virus (HIV) infection is the determining factor in the development of acquired immunodeficiency syndrome (AIDS). At present there is no effective vaccine against this disease. The objectives of this project are to characterize HIV antigens, determine the targets of humoral and cell mediated immunity, and to use this information to develop candidate vaccines. We have constructed recombinant vaccinia viruses containing genetic information of HIV and the closely related simian immunodeficiency virus. These recombinant viruses have been used to prepare purified immunogens, monoclonal antibodies, targets for cytotoxic T cells and candidate vaccines.